Time-Synchronized Control-Channel Multiplexing Scheme Using Cyclic-Shifted Zadoff-Chu Sequences for Full Duplex

This paper proposes a time-synchronized control-channel multiplexing scheme using cyclic-shifted Zadoff-Chu sequences for full duplex (FD) aiming at decreasing the latency due to feedback control signals. In the proposed scheme, a set of different cyclic-shift resources of a Zadoff-Chu sequence with the same root index are assigned to control signals in both the downlink and uplink that are multiplexed in time-synchronized subframes accompanied with a cyclic prefix and cyclic suffix. Because the cross-correlation of the different cyclic-shifted Zadoff-Chu sequences with the same root index is quite low, the self-interference (SI) or co-channel interference (CCI) that leaks from its own transmitter or that of another set of user equipment to a receiver is suppressed to a very low level after despreading in the frequency domain. As a result, the significantly reduced SI or CCI after despreading results in a decreased level of complexity for the SI or CCI canceller, i.e., particularly the digital interference canceller. The computed cross-correlation results show that the cross-correlations among different cyclic-shift indices become almost zero. Based on the computed cross-correlations of the cyclic-shifted Zadoff-Chu sequences, we discuss the receiver structures including SI rejection methods for a base station and UE. Because control signals are multiplexed in every subframe in the downlink and uplink, the proposed control-channel multiplexing is applicable to low-rate control signals that require low latency.